Power and Seat Height

bill · May 19, 2007

Therefore, I'm guessing here, if your CG is way aft while trying to sprint you'd be less efficient and produce less power. If that is true then the same can be said about being seated which fore and aft position has a direct effect.

why do you think that being aft would negatively affect your ability to produce power? The longer extension makes it harder to maintain a higher cadence, I think, but I don't think that the CG position itself matters to this.

This is one of those sacred cow issues for which there just isn't any evidence, other than "years of experience," "how can 14 million Frenchman be wrong?" etc., etc.

woodys737 · May 19, 2007

bill said:
why do you think that being aft would negatively affect your ability to produce power? The longer extension makes it harder to maintain a higher cadence, I think, but I don't think that the CG position itself matters to this.

This is one of those sacred cow issues for which there just isn't any evidence, other than "years of experience," "how can 14 million Frenchman be wrong?" etc., etc.

I was thinking in the context of chasing a break down. While seated in your "normal" position what would happen to power output if your seat were able to slide back 10cm? 20cm? Rediculous, but I made a poor attempt to try and convey that at some point fore/aft position will effect CG. Thus, at some point, fore/aft will effect power too.

I'm going to a race, so ya'll have a great week-end!

bill · May 19, 2007

woodys737 said:
I was thinking in the context of chasing a break down. While seated in your "normal" position what would happen to power output if your seat were able to slide back 10cm? 20cm? Rediculous, but I made a poor attempt to try and convey that at some point fore/aft position will effect CG. Thus, at some point, fore/aft will effect power too.

I'm going to a race, so ya'll have a great week-end!

but moving back wouldn't affect power because you've moved your center of gravity, it would affect power because at some point you can't reach the pedals.

have a good race.

Eric_H · May 20, 2007

iliveonnitro said:
Kerry is advocating 1.08 or 1.10*inseam height, whereas the Guimard is .882*inseam. This is a big difference. For me, the difference between these two formulae is a 72.9cm saddle height and 90.8cm saddle height. Uh, 18cm difference? Either of you care to clarify?

bill already addressed this, but the Guimard/Lemond is from the center of the BB to top of the saddle. The 1.08-1.10 number is from the top of the pedal surface to the top of the saddle, with the crank arm down and in line with the seat tube. It should be noted that with the variations in shoe sole thickness and the distance from the outer sole to the center of the pedal spindle, both of these methods are not absolutes, but decent ballpark starting points.

iliveonnitro said:
Whoever posted saying that saddle fore-aft doesn't affect power: I completely disagree. Try moving your saddle back .5" (and seat height lower to compensate) and do a 2 minute interval. Now move it back to original and forward .5" (seat higher to compensate) and do a 2 min interval. Which has more power? I guarantee the forward position will.

During hard efforts, do you notice that you (and pros) wind up sliding forward on the seat? This is, to a lesser degree, similar to standing. This can affect many things, but a big one (mentally referencing Bicycling Science, 3rd edition, MIT Press) is that moving forward in the saddle puts your position more directly over the bottom bracket. This translates to more power to the pedals. It also increases the tendency to mash. In the long run, there is back pain, too.

Many bike fitters get saddle fore-aft wrong. When using a plumb line, you should not measure from the top of the knee. If you straighten your leg and pinch the patella on each side of the knee--that should be the reference point. This is another reason why most people slide too far forward on their saddle during normal riding conditions...improper fitting.

Regarding fore-aft, I think your assumption that more power is produced by being more "over the top" of the cranks (this is a sentiment also conveyed further along in this thread) is not exactly correct. You are considering power produced over one type of interval, but road racing happen on variable terrain. Racers (including pros) do move forward in certain situations, but I think you will find that it is usually to facillitate faster pedaling in very fast situations, while deep in the drops. This generally will allow the rider to pedal at a higher cadence and might increase peak power. Conversely, they tend to push rearward during climbing to enhance the ability to push a larger gear. This has the effect of lengthening the saddle-pedal distance and allowing more leg extension. I cannot say for certain because I am not a power meter junkie, but I would guess for extended periods power the rearward position will produce a higher average power.

Mark McM · May 22, 2007

"Sitting on the rivet"

iliveonnitro said:
During hard efforts, do you notice that you (and pros) wind up sliding forward on the seat? This is, to a lesser degree, similar to standing. This can affect many things, but a big one (mentally referencing Bicycling Science, 3rd edition, MIT Press) is that moving forward in the saddle puts your position more directly over the bottom bracket. This translates to more power to the pedals. It also increases the tendency to mash. In the long run, there is back pain, too.

I think if you examine it more closely, the tendency to "sit of the rivet" (i.e. slide forward on the saddle) during hard efforts is due to something else entirely. When a rider is going all out, they tend to use their upper body and arms more, pulling on the handlebars. Normally, riders tend to ride with just a slight bend to the elbows, but actively pulling on the handlebars is more effective with more bend in the elbow. Thus, riders who are riding hard bend their elbows more, pulling themselves closer to the handlebars, and thus sliding forward on the saddles.

bill · May 22, 2007

Mark McM said:
I think if you examine it more closely, the tendency to "sit of the rivet" (i.e. slide forward on the saddle) during hard efforts is due to something else entirely. When a rider is going all out, they tend to use their upper body and arms more, pulling on the handlebars. Normally, riders tend to ride with just a slight bend to the elbows, but actively pulling on the handlebars is more effective with more bend in the elbow. Thus, riders who are riding hard bend their elbows more, pulling themselves closer to the handlebars, and thus sliding forward on the saddles.

I think that this is exactly right. I was thinking about it today, at lunchtime, as I sat on the rivet trying to chase down some f*ckers who had increased a gap from 20 m to 150 m by beating a light. f*ckers.

Mark McM · May 22, 2007

Sliding back in the saddle for climbing

Speedy said:
You must not race.

Trust me, people don't ride on the rivet for comfort. Being over the cranks is more powerful than behind them - period.

Maybe you race, but you must not actually watch racers - or else you'd know that in some situations, racers tend to push themselves further back, behind the cranks, not further forward, to generate power.

In particular, many riders tend to sit back in the saddle when climbing. This is for several reasons:

- Moving back in the saddle tends to increase leg extension, increasing leg force. Many riders tend to decrease cadence when climbing, and compensate by increasing pedal force. The rearward position is not as conducive for high cadence spinning, but can produce higher pedal force.

- Many riders climb in the bar tops. This decreases handlebar reach by 100 mm or so. To compensate, riders tend to sit further back in the saddle.

As mentioned in the previous post, sitting on the nose of the saddle is often more a case of accomodating a more compact upper body position (i.e. elbows bent to pull on the handlebars), rather than a desire to get over the pedals.

levels1069 · May 22, 2007

ehhh i'm gonna have to go ahead and disagree with the general thought here...

look at lots of TT riders or triathletes, even for being as aero as possible...the main point is to still try to stay as much centered over the BB as possible. They creep forward on the saddle to stay over the bottom bracket, which stresses your quads more and alows more explosive power. lots of great riders also center themselves over the BB when climbing, moving forward on the saddle. Specifically Jens Voight, Jan Ulrich, Levi Leipheimer...all very powerful guys

bill · May 22, 2007

levels1069 said:
ehhh i'm gonna have to go ahead and disagree with the general thought here...

look at lots of TT riders or triathletes, even for being as aero as possible...the main point is to still try to stay as much centered over the BB as possible. They creep forward on the saddle to stay over the bottom bracket, which stresses your quads more and alows more explosive power. lots of great riders also center themselves over the BB when climbing, moving forward on the saddle. Specifically Jens Voight, Jan Ulrich, Levi Leipheimer...all very powerful guys

I don't believe that the forward position has anything to do with engaging the quads or explosive power or whatever. If you have any evidence for your contention, bring it here, because I've heard of this for years and it makes no sense and no one has any support. I understand that people still believe it, but, for example, people have believed and believe to this day that lactic acid causes muscle failure and it just isn't true and it has been known not to be true for a really long time.

The forward position of TT bikes mostly has to do with one issue -- by moving the pelvis forward in relation to the BB, the rider can get flatter and lower on the bike and still maintain the same hip/femur orientation through the pedal stroke. The other adjustments to TT frame geometry have to do with trying to keep as much of the rider's weight back from the front as possible, to add some stability and handling, which is why road frames don't convert very well to TT frames.

footballcat · May 24, 2007

go get fit, i was fit and they measured the angle of ankle to the knee to hip, and 140 degrees to 145 is what he was looking for i belive. I couldnt be happier, solved some of my knee issues, and im comfy on the bike, i do have 13cm of drop though.

estone2 · May 24, 2007

bill said:
this is an extraordinary claim. do you have any evidence of this? this would be quite a revelation.

Look at Dave Z during a time trial.
The position provides more TT-effort type power, as it activates the quads more (or something?). It's very good for on the flats, if you're going solo, butchering yourself.

However, the position SUCKS for climbing. As such, it's not a good position to set your bike up with - no point in getting to the climb really fast and then getting slaughtered.

-estone2

bill · May 24, 2007

the position is aerodynamic. it doesn't "activate the quads" (or it would likely be good for climbing, no?)

Speedy · May 24, 2007

I use to ride on the front only for flat hammering, but after I seeing a number of pros sitting more on the front while climbing, I’ve been doing it too. It depends on the length of the climb, but for a 30min or less - get to the top as fast as you can climb, I seem to get more power there than my usual slid back, sustained climbing position.

bill · May 24, 2007

Speedy said:
I use to ride on the front only for flat hammering, but after I seeing a number of pros sitting more on the front while climbing, I’ve been doing it too. It depends on the length of the climb, but for a 30min or less - get to the top as fast as you can climb, I seem to get more power there than my usual slid back, sustained climbing position.

Okay, against all evidence, you all are going to insist on this, so I guess I'll give up.
If it works for you, you go ahead.
But here's food for thought -- I sincerely question whether you can detect someone, anyone, shifting their weight forward from watching them. standing? that's different; I'm talking about shifting forward that cm or two or three that we all know as on the rivet.
and maybe you're climbing better because you just got stronger?

Speedy · May 24, 2007

bill said:
...and maybe you're climbing better because you just got stronger?

True that.

When I watch others riders, I’m looking at how much saddle is sticking out the back - compared to their other positions, and how upright their torso is. Moving forward brings you more upright when climbing.

bill · May 24, 2007

Speedy said:
True that.

When I watch others riders, I’m looking at how much saddle is sticking out the back - compared to their other positions, and how upright their torso is. Moving forward brings you more upright when climbing.

although moving forward is also a function of pulling back on the bars, which tends to happen when the climber is, as they say, under pressure.

I still don't think it has anything to do with increasing your power per se. you do shorten the extension a little, which makes it easier to spin, but shortening the extension is generally considered to lessen the force you can apply, not increase it, although I suppose if you maintain the same force but increase the cadence, thereby applying that force more times in a given period of time, you're going to go up faster. But it's not going to help you if you are maintaining the same cadence.

Power and Seat Height

bill

woodys737

bill

Eric_H

Mark McM

bill

Mark McM

levels1069

bill

footballcat

estone2

bill

Speedy

bill

Speedy

bill

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